CCTV Systems
When designing an arrangement for a set of sensors, e.g., cameras in a closed-circuit television (CCTV) surveillance system, the pose of all sensors, which we refer to as the sensor arrangement, can have a dramatic impact on a cost and effectiveness of the system. As defined herein the pose is the 3D location and 3D orientation of each sensor.
This is especially true for large-scale sensor deployments that can number in the thousands of sensors. Furthermore, as mechanisms, security or otherwise, facilitated by the sensors become more sophisticated, more stringent constraints need to be taken into account to ensure system effectiveness. For example, issues such as spatial resolution and angular resolution of certain 3D locations can mean the difference between the successful deployment of a face-recognition system.
Sensor coverage describes the locations the sensor can sense, taking into account occlusions for instance, and how well the sensor can sense a given location. Measures, such as spatial resolution and angular resolution, can be used to quantify sensor coverage at a given location.
Coverage Analysis
Coverage analysis is derived from a computational geometry problem commonly referred to as the art gallery problem, where the goal is to place a minimum number of guards (human sensors), such that all locations in the gallery can be observed. The art gallery problem is considered non-deterministic polynomial-time (NP) hard.
However, theoretical computational geometry approaches do not take into account the physical, real-world nature of the applied problem of generating effective sensor arrangements. Nevertheless, most conventional approaches place sensors in an environment according to a 2D floor plan, and only use 2D data to determine sensor coverage.
FIG. 1A, for a top view, shows a result of a conventional 2D coverage analysis of an environment 120 by a sensor 211 based on a 2D floor plan. This includes an area 130 that is considered adequately covered, as well as an area that is occluded 129 due to a wall 121. However, coverage analyses based on just a 2D floor plan can leads to errors in coverage data due to objects that cannot be well represented accurately in the 2D floor plan, for example, a partial-height vertical wall 140, which can cause an error in the coverage analysis for an area 110 behind the partial-height wall.
FIG. 1B shows, for a side view, the coverage ‘holes’ that can be introduced when the 2D coverage analysis is based only on a 2D floor plan. Here, a vertical cross-section shows that the partial-height wall 140 introduces an area 110 that is not covered by the camera despite that the 2D analysis considers the area 110 covered, see FIG. 1A.